The compounds of formula I are described as 11,12-seco-prostaglandins because of their structural relationship to the naturally occurring prostaglandins.
The prostaglandins constitute a biologically prominent class of naturally occurring, highly functionalized C.sub.20 fatty acids which are anabolized readily in a diverse array of mammalian tissues from three essential fatty acids; namely, 8,11,14-eicosatrienoic acid, 5,8,11,14-eicosatetraenoic acid and 5,8,11,14,17-eicosapentaenoic acid. Each known prostaglandin is a formal derivative of the parent compound, termed "prostanoic acid"; the latter is a C.sub.20 fatty acid covalently bridged between carbons 8 and 12 such as to form a trans, vicinally substituted cyclopentane in which the carboxy-bearing side chain is "alpha" or below the plane of the ring and the other side chain is "beta" or above the plane of the ring as depicted in formula III: ##SPC3##
The six known primary prostaglandins, PGE.sub.1, PGE.sub.2, PGE.sub.3, PGF.sub.1.sub..alpha., PGF.sub.2.sub..alpha., and PGF.sub.3.sub..alpha. resulting directly from anabolism of the above cited essential fatty acids via the action of prostaglandin synthetase, as well as the three prostaglandins resulting from in vivo dehydration of the PGE's, i.e., PGA.sub.1, PGA.sub.2, and PGA.sub.3, are divided into three groups; namely, the PGE, PGF, and PGA series on the basis of three distinct cyclopentane nuclear substitution patterns as illustrated as follows:
______________________________________ ##STR2## ##STR3## ##STR4## PG R.sub.a R.sub.b ______________________________________ E.sub.1, F.sub.1, A.sub.1 ##STR5## ##STR6## E.sub.2, F.sub.2, A.sub.2 ##STR7## ##STR8## E.sub.3, F.sub.3, A.sub.3 ##STR9## ##STR10## E.sub.o, F.sub.o, A.sub.o ##STR11## ##STR12## ______________________________________
It should be noted that the Arabic subscripts designate the number of carbon-carbon double bonds in the designated compound and that the Greek subscript used in the PGF series designates the stereochemistry of the C-9 hydroxyl group.
Although the prostaglandins were discovered independently in the mid-1930's by Goldblatt [J. Chem. Soc. Chem. Ind. Lond., 52, 1056 (1933)] in England and Von Euler [Arch. Exp. Path. Pharmark., 175, 78 (1934)] in Sweden, these complex natural products received little attention from the scientific community until the early 1960's which coincides with the advent of modern instrumentation (e.g., mass spectrometry) which, in turn, was requisite for their successful isolation and structural elucidation by Bergstrom and colleagues [see Angew. Chem. Int. Ed., 4, 410 (1965) and references cited therein for an account of this work]. Within the last decade, a massive international scientific effort has been expended in developing both biosynthetic and chemical routes to the prostaglandins and, subsequently, in investigating of their biological activities. During this period, prostaglandins have been shown to occur extensively in low concentrations in a myriad of mammalian tissues where they are both rapidly anabolized and catabolized and to exhibit a vast spectrum of pharmacological activities including prominent roles in (a) functional hyperemia, (b) the inflammatory response, (c) the central nervous system, (d) transport of water and electrolytes, and (e) regulation of cyclic AMP. Further details concerning the prostaglandins can be found in recent reviews of their chemistry [J. E. Pike, Fortschr. Chem. Org. Naturst., 28, 313 (1970) and G. F. Bundy, A. Rep. in Med. Chem., 7, 157 (1972 )], biochemistry [J. W. Hinman, A. Rev. Biochem., 41, 161 (1972)], pharmacology [J. R. Weeks, A. Rev. Pharm., 12, 317 (1972)], physiological significance [E. W. Horton, Physiol. Rev., 49, 122 (1969)] and general clinical application [J. W. Hinman, Postgrad. Med. J., 46, 562 (1970)].
The potential application of natural prostaglandins as medicinally useful therapeutic agents in various mammalian disease states is obvious but suffers from three formidable major disadvantages, namely, (a) prostaglandins are known to be rapidly metabolized in vivo in various mammalian tissues to a variety of metabolites which are devoid of the desired original biological activities, (b) the natural prostaglandins are inherently devoid of biological specificity which is requisite for a successful drug, and (c) although limited quantities of prostaglandins are presently produced by both chemical and biochemical processes, their production cost is extremely high; and, consequently, their availability is quite restricted.
Our interest has, therefore, been to synthesize novel compounds structurally related to the natural prostaglandins but with the following unique advantages: (a) simplicity of synthesis leading to low cost of production; (b) specificity of biological activity which may be either of a prostaglandin-mimicking or prostaglandin-antagonizing type; (c) enhanced metabolic stability. The combination of these advantages serves to provide effective, orally and parenterally active therapeutic agents for the treatment of a variety of human and animal diseases. Included are applications in renal, cardiovascular, gastrointestinal, respiratory, and reproductive systems, and in the control of lipid metabolism, inflammation, blood clotting, skin diseases, growth hormone release, selected cancers, and certain autoimmune diseases.
More specifically, in the clinic, prostaglandin agonists can function as agents for improving renal function (e.g., renal vasodilation), antihypertensives, anti-ulcer agents, agents for fertility control, antithrombotics, antiasthmatics, antilipolytics, antineoplastic agents, agents for the treatment of certain skin diseases, drawfism, and autoimmune diseases.
Prostaglandin antagonists can function as antiinflammatory agents, anti-diarrheal agents, antipyretics, agents for prevention of premature labor, and agents for the treatment of headache.
The compounds of this invention are particularly useful in the area of fertility control. In animals, they can be used for estrus synchronization, and treatment of infertility due to persistence of luteal function. In humans, they can be used as postcoital contraceptive agents which function by induction of menses.
Further, the compounds of this invention by virtue of their marked activity in inhibiting the aggregation of blood platelets are of potential usefulness as antithrombotic agents.
The compounds of this invention can be administered either topically or systemically, i.e., intravenously, subcutaneously, intramuscularly, orally, rectally, or by aerosolization in the form of sterile implants for long action. They can be formulated in any of a number of pharmaceutical compositions and non-toxic carriers to this end.
The pharmaceutical compositions can be sterile injectable suspensions or solutions, or solid orally administrable pharmaceutically acceptable tablets or capsules; the compositions can also be intended for sublingual administration, or for suppository use. It is especially advantageous to formulate compositions in dosage unit forms for ease and economy of administration and uniformity of dosage. "Dosage unit form" as a term used herein refers to physically discrete units suitable as unitary dosages for animal and human subjects, each unit containing a predetermined quantity of active material calculated to produce the desired biological effect in association with the required pharmaceutical means.
Illustratively, a sterile injectable composition can be in the form of aqueous or oleagenous suspensions or solutions.
The sterile injectable composition can be aqueous or oleagenous suspension or solution. Suspensions can be formulated according to the known art using suitable dispersing and wetting agents and suspending agents. Solutions are similarly prepared from the salt form of the compound. For the laboratory animals, we prefer to use incomplete Freund's adjuvant or sterile saline (9%) as carrier. For human parenteral use, such as intramuscularly, intravenously, or by regional perfursion, the diluent can be a sterile aqueous vehicle containing a preservative; for example, methylparaben, propylparaben, phenol, and chlorobutanol. The aqueous vehicle can also contain sodium chloride, preferably in an amount to be isotonic; as well as a suspending agent, for example, gum arabic, polyvinyl pyrrolidone, methyl cellulose, acetylated monoglyceride (available commercially as Myvacet from Distillation Products Industry, a division of Eastman Kodak Company), monomethyl glyceride, dimethyl glyceride or a moderately high molecular weight polysorbitan (commercially available under the tradenames Tween or Span from Atlas Powder Company, Wilmington, Delaware). Other materials employed in the preparation of chemotherapeutic compositions containing the compound may include glutathione, 1,2-propanediol, glycerol and glucose. Additionally, the pH of the composition is adjusted by use of an aqueous solution such as tris(hydroxymethyl)aminomethane (tris buffer).
Oily pharmaceutical carriers can also be used, since they dissolve the compound and permit high doses. Many oily carriers are commonly employed in pharmaceutical use, such as, for example, mineral oil, lard, cottonseed oil, peanut oil, sesame oil, or the like.
It is preferred to prepare the compositions, whether aqueous or oils, in a concentration in the range of from 2-50 mg./ml. Lower concentrations require needless quantities of liquid. Higher concentrations than 50 mg./ml. are difficult to maintain and are preferably avoided.
Oral administration forms of the drug can also be prepared for laboratory animals or human patients. The same dosage levels can be used as for injectable forms. Generally, a solid unit dosage form can be prepared containing from 0.5 mg. to 25 mg. active ingredient.
Whatever the mode of administration, doses in the range of about 0.10 to 20 milligrams per kilogram of body weight administered one to four times per day are used, the exact dose depending on the age, weight, and condition of the patient, and the frequency and route of administration.
The low cost and ready accessibility of the compounds of this invention make them particularly promising for applications in veterinary medicine. In particular, their luteolytic properties make them useful as agents for estrus synchronization in cattle, horses and other farm animals.